It is well known that systemic blood pressure oscillates with low(0.04~0.1Hz), mid(0.1~0.15Hz), and high(respiratory) frequency range. But there has been no study about oscillation of pulmonary artery pressure(PAP).

We measured PAP for 5 minutes in 32 patients of ventricular septal defect and stored them to computer files. Power spectral density curve was obtained. Low, mid, respiratory frequency power were measured by integrating the area within each frequency range below the power density curve.

The incidence of significant low frequency power(more than 5% of total power) were higher in patients of high PAP and hign Rp/Rs than those of low PAP and Rp/Rs(p<0.01 and p<0.005 respectively). The low frequency power positively correlates with PAP and Rp/Rs(r=0.62, p<0.0005 and r=0.61, p=0.0005 respectively).

It can be said conclusively that as PAP and pulmonary vascular resistance elevates, the PAP tends to definitively oscillate in low frequency range.